1. Field of the Invention
The present invention relates to a rotating electric machine particularly provided with an improved rotor cooling structure for reducing pressure loss in ventilation ducts of a rotor.
2. Related Art
A general rotating electric machines, for example, a rotor structure of a turbine generator, is shown in FIGS. 13 to 15, in which FIG. 13 is a cross-sectional view illustrating a structure of an upper portion of a rotor core, FIG. 14 is an enlarged view illustrating a coil slot section in FIG. 13, and FIG. 15 is a longitudinal sectional view illustrating a structure of one side of a rotor in an axial direction.
With reference to FIG. 13, a plurality of coil slots 2 are provided on a rotor core 1 in a circumferential direction along an axial direction thereof, and in the coil slot 2, a rotor coil 4 is housed.
As illustrated in FIG. 13, the rotor coil 4 that is formed by laminating a plurality of field conductors 11 is housed in the coil slot 2. A rotor is formed by inserting a rotor wedge 6 in an opening end portion of the coil slot 2 and supporting the rotor coil 4. Further, as illustrated in FIG. 14, a portion of the rotor coil 4, which is protruded from an end portion of the rotor core 1 in the axial direction, is held by a support ring 9 from the outside.
Insulation materials 5 are inserted to ensure insulation of the rotor coil 4, respectively, between the rotor coil 4 and the rotor core 1, between the rotor coil 4 and the rotor wedge 6, and between the rotor coil 4 and the support ring 9. Further, although not portionicularly illustrated, the insulation materials 5 are also inserted between field conductors 11, respectively.
Furthermore, a sub-slot 3 for distributing a cooling gas 8 in the rotor axis direction is provided on a rotor inner circumferential side in the coil slot 2. In the sub-slot 3, the cooling gas 8 is distributed to cool the rotor coil 4.
As illustrated in FIG. 14, a coil ventilation duct 7 is formed to introduce the cooling gas 8 from the end portion of the rotor core 1 into the sub-slot 3 provided toward a central portion of the rotor core 1 from the end portion of the rotor core 1 and to distribute the introduced cooling gas 8 in the coil slot 2 from the side of an inner diameter to the side of an outer diameter of the rotor core 1. A channel for the cooling gas 8 for cooling the rotor coil 4 is formed by arranging the coil ventilation duct 7 along the axial direction so that the coil ventilation duct 7 passes through the rotor coil 4, the insulation materials 5, and the rotor wedge 6 in a radial direction and communicates with the sub-slots 3 provided over the entire length of the rotor core 1.
The cooling gas 8 is introduced, due to a centrifugal fan effect by the rotation of the rotor, as illustrated by arrows in FIG. 15, into the sub-slot 3 from the end portion of the rotor core 1, flows toward the central portion of the rotor core 1, and sequentially branches to the coil ventilation ducts 7.
The cooling gas 8 passing through the coil ventilation ducts 7 cools and absorbs heat generated in the rotor coil 4, and the cooling gas 8 is discharged to the side of the outer diameter of the rotor core 1 through the coil ventilation ducts 7 arranged in the rotor wedge 6.
As a cooling method of cooling the rotor coil 4 that has the sub-slots 3 for introducing the cooling gas 8, in addition to the structure illustrated in FIG. 15, various methods have been proposed. For example, Japanese Patent No. 3564915 discloses a method of dividing a coil ventilation duct into a plurality of ducts, Japanese Patent No. 3736192 discloses a method of forming an oblique opening, and Japanese Unexamined Patent Application Publication No. 7-170683 discloses a method of ventilating in an axial direction.
In the above-described rotating electric machines, an upper limit of temperature of the rotor coil 4 is strictly regulated in consideration of the heat resistance performance of the insulation materials which form the rotor coil 4. Accordingly, while current density of the rotor coil 4 increases as single capacities of recent rotating electric machines increase, in order to reduce the coil temperature to a temperature lower than the heat resistance temperature of the insulating materials 5, it is necessary to increase a diameter of the rotor, increasing a length of the core or the like so as to reduce heat volume by inserting more field conductors 11 into the coil slot 2 in the rotor.
Further, it is necessary to keep wider a ventilation area for increasing the cooling gas 8 and to increase the cooling performance, which increases the size of the generator.
In the ventilating and cooling system provided with the sub-slots 3, all cooling gas 8 in the coil ventilation duct 7 connected to the sub-slot 3 passes through in a concentrated manner in each of the sub-slots 3 from the inlet at the end portion of the rotor core 1 to the rotor coil ventilation duct 7 of the most core end side. Accordingly, the flow velocity is fast and causes large pressure loss. Then, if the duct cross-sectional area of the coil ventilation duct 7 or the number of the ducts is increased, it is impossible to ensure the ventilation amount of the cooling gas 8 for cooling the inside of the rotor coli 4.
Further, if the capacity of the rotating electric machine is increased and the length of the core of the rotating electric machine is increased, the length of the sub-slot 3 in the axial direction is increased, and pressure loss in the sun-slot 3 is also increased. Accordingly, the cooling gas 8 is hardly to flow.
Especially, in a case of an air-cooling system using air as the cooling gas 8, a heat capacity of the cooling gas 8 becomes small and temperature rise of the cooling gas 8 becomes large. Accordingly, it is necessary to keep the cooling gas 8 as much as possible.
In these systems, as a method of improving the cooling performance, like the method disclosed in the above-described Japanese Patent No. 3564915, the method of dividing the coil ventilation duct 7 into the plurality of ducts so as to extend the heat transfer area has been proposed. However, a rate of increase in the amount of the cooling gas 8 to a rate of increased area of the coil ventilation ducts 7 becomes small. Accordingly, the flow velocity in the coil ventilation ducts 7 is decreased, and the heat transfer rate is reduced, resulting in the deterioration of the cooling performance.
Furthermore, by dividing the coil ventilation duct 7 in the ducts, a flow rate distribution between the coil ventilation ducts can be easily generated, so that it is highly possible to locally increase the temperature of the rotor coil 4.
As the other methods or systems, for example, Japanese Unexamined Patent Application Publication No. 2001-178050 discloses a cross-sectional area of the flow channel of the sub-slot 3 formed to be small as approaching to the central portion of the rotor core 1 to prevent the flow rate at the central portion of the rotor core 1 from being increased more than required. In the method, temperature homogenization of the coil temperature can be achieved. However, a ventilation resistance in the sub-slot 3 is increased. Accordingly, a total amount of the cooling gas is reduced and an average temperature of the rotor coil 4 is increased.
Furthermore, there is proposed a method of increasing the ventilation amount of the cooling gas 8 by reducing inlet loss in the sub-slot 3, for example, in Japanese Unexamined Patent Application Publication No. 11-150898 and Japanese Unexamined Patent Application Publication No. 2001-258190. In these methods, there is reduced a large pressure loss generated when the cooling gas 8 flows at a large inflow angle into an opening of the sub-slot 3 which is rotating at a very high speed. For example, the inlet portion of the sub-slot 3 is formed to be a smooth R-shape such that the cooling gas is easy to flow in, or a groove for introducing the cooling gas 8 is formed on a rotor shaft 10 provided outside the end portion of the rotor core 1.
However, because of limitations in sizes of adjacent coil slots 2 or sub-slot 3, it is very difficult to turn and introduce the cooling gas 8 in the inside of the sub-slot 3 while reducing the loss at the large inflow angle, and therefore, it is difficult to expect a large pressure loss reduction effect.